In mobile radio networks, an operative identity code is generally passed by a mobile station to the fixed network part at the start of each communication transaction. This operative identity code generally identifies the user to the network and for this purpose, each user is assigned a unique identity code. However, it is undesirable to have all the transactions of a user marked by the user's unique identity code since this permits the user's activity to be monitored by listening to the network radio traffic. For this reason, temporary identity codes are allocated to users by the fixed network part, the fixed network part being itself aware of the association between the temporary and unique identity codes of a user; the temporary identity code is then used by a user's mobile station as its operative identity code when initiating a transaction.
In principle, it should be a simple matter for the network operator to ascertain the current operative identity code being used by a user as the network infrastructure is already aware of the association. However, as a practical matter, accessing the information held in the network infrastructure for non-standard purposes requires substantial modification to existing software with the consequent need to re-qualify the software and associated systems.
It is therefore an object of the present invention to provide an alternative way of tracking the current operative user identity of a particular user.
As will be more fully set out below, the present invention involves providing a monitoring method and apparatus that derives the sought-after information by monitoring signalling messages on the network rather than by accessing data stored in the network infrastructure. Monitoring signalling messages to derive information on a mobile network is not new in itself and may be done using, for example, the Hewlett-Packard 37900D Signalling Test Set. However, not only is it previously unknown to seek to ascertain the current operative identity code being used for a user by monitoring network signalling messages, but the required information to track the current operative identity code is generally not contained in an individual messages but is spread across different messages.